Solar-electric systems have become more and more common, and of greater and greater importance. The use of solar-electric systems is expected to increase, potentially dramatically.
Energy from solar-electric systems designed for on-site usage (e.g., residential systems) can exceed energy usage and such energy can be supplied to an external power source, e.g., a power grid. However, in many systems, at least part of the time (e.g., at night), energy from such solar-electric systems needs to be supplemented, e.g., by energy from a power grid.
In situations where a power load is supplied to a site facility from more than one source (e.g., from one or more solar-electric systems and from one or more external power source), it would be of great value to have a simple way of sensing the total magnitude of power being consumed by the site facility, the total quantity of energy consumed by the site facility over time intervals, the instantaneous level of power being produced by the (or each) energy-producing system, and the quantity of energy produced by the (or each) energy-producing system over time intervals.
In cases where a grid-connected site facility (e.g., a home or other premises) is supplied with energy from one or more energy-producing systems, such as a solar-electric system, there is a need for a simple way of sensing the total amount of power and energy being consumed by the site facility (i.e., the total consumed, whether supplied from an energy-producing system, from the power grid, or any combination thereof) as well as the amount of power and energy being produced by the (or each) energy-producing system (whether the energy produced is supplied to a circuit within the site facility, to an external power source, or to any combination thereof).
In addition, there is a need to be able to determine when an energy-producing system is not functioning properly, i.e., when it is producing less energy than it should be producing under prevailing conditions.